Initial defecation time and rate of passage of digesta in adult Hawaiian monk seals, Monachus Gwen D. Goodman-Lowe, Shannon Atkinson, and James R. Carpenter Abstract: In an effort to gain a better understanding of the digestive physiology of the Hawaiian monk seal, Monachus schauinslandi, we measured initial defecation time and rate of passage of digesta using chromic oxide (Cr,O,) and frozen corn kernels as markers. Initial defecation time ranged from 9,5 to 19 h (mean 14 + 4,8 h), which was a longer period of time than that reported for any other pinniped. The rate of passage of digesta measured using a single-pulse dose of Cr,O, was approximately 39 h for two of the three seals, which is also longer than that reported for other pinnipeds. Possible reasons for these longer rates include morphological and physiological differences, age of the seals, and feeding regime.. Percent Cr,O, recovery was low (52.7-74.8%), reflecting the difficulty in collecting liquid stools. Levels of protein and ash (dry matter basis) were 21.70 and 34.79%, respectively, which reflects the high protein and mineral contents of the herring diet. This study yielded essential base-line data that will provide further insight into the digestive physiology of the Hawaiian monk seal. Rdsumd : Afin de mieux comprendre la physiologie de la digestion chez le Phoque-moine d'Hawaii, Monachus schauinslandi, nous avons enregistrk le temps kcoulk avant la premiere dkfecation et la durke du passage du bol alimentaire en utilisant de l'oxyde de chrome (Cr,O,) et des grains de mai's surgelks comme marqueurs. La durke de la digestion avant la premikre dkfkcation se situait entre 9,5 et 19 h (moyenne 14 + 4,8 h), pkriode plus longue que celle enregistrke chez d'autres pinnipkdes. La durke du passage du bol alimentaire, kvaluke par utilisation d'une seule dose de Cr,O,, a kt6 de 39 h environ chez deux des trois phoques, une duree plus longue que celle rapportee pour d'autres pinnipkdes. Parmi les raisons que nous pouvons invoquer pour expliquer ces durees inusitees, il faut penser a des diffkrences morphologiques et physiologique, a I'iige et au rkgime alimentaire. La rkcupkration du Cr,O, a kt6 faible (52,7-74,8%) a cause de la difficult6 de prklever des feces liquides. Les concentrations de protkines et de cendre (base des matikres skches) ont kt6 kvalu6es a 21,70 et 34,79% respectivement, ce qui reflkte les contenus elev6s en protkines et en minkraux du rkgime de harengs. Ces rksultats constituent des donnkes de base essentielles qui permettront de mieux comprendre la physiologie de la digestion chez le Phoque-moine d'Hawaii. [Traduit par la Rkdaction] Introduction ing of defecation of the marker and yield a cumulative excre- The feeding ecology of pinnipeds is complex and requires knowledge of an animal's natural prey, along with compre- hension of its digestive physiology. Partial understanding of this physiology may be accomplished by measuring both the initial defecation time (IDT) and rate of passage of digesta in the animal. The IDT, also reported as transit time, refers to the elapsed time between ingestion of a marked meal and its first appearance in the feces (Helm 1984). Rate of passage refers to the time required for the entire marked meal to pass through a point in the digestive tract in a given time (Kotb and Luckey 1972). Both of these methods require continuous collection of the feces along with records of the precise tim- Received May 24, 1996. Accepted October 30, 1996. G.D. Goodman-Lowe' and S. Atkinson. Hawaii Institute of Marine Biology, University of Hawaii, Box 1346, Kaneohe, HI 97644, U.S.A. J.R. Carpenter. Department of Animal Sciences, 1800 East-West Road, University of Hawaii, Honolulu, HI 96822. U.S.A. ' Author to whom all correspondence should be addressed (e-mail: glowe@hawaii.edu). tion curve with a sigmoid shape. Rate of digestion and assimilation efficiency studies have been conducted on a variety of terrestrial animals, including bobcats (Golley et al. 1965), lizards (Nagey 1977), and birds (Speakman 1987), where collection of feces is straightforward. However, col- lection of feces from aquatic species is difficult, and this may be reflected by the relatively few rate of passage studies con- ducted on pinnipeds. From the few studies concerning IDT or transit times and digestion rates (Helm 1984; Markussen 1993; Krockenberger and Bryden 1994), it is apparent that both of these parameters are affected by multiple variables such as length of the gastrointestinal tract, metabolic rate, frequency of feeding, and activity level, and may also be species or diet specific. Studies on prey preferences of pinnipeds commonly use either stomach content analysis and (or) analysis of prey remains from fecal samples collected on land. The distance offshore to which the animals travel when foraging, com- bined with their rates of digestion, will directly affect the composition of the samples that are used for prey-preference studies. Thus, studies of the rate of passage of digesta are needed to validate foraging studies, especially in Hawaiian monk seals, which have been shown to forage several kilo- Can. J. Zool. 75: 433-438 (1997) @ 1997 NRC Canada Can. J. Zool. Downloaded from www.nrcresearchpress.com by Hunan Normal University on 06/03/13 For personal use only.